1. Field of the Invention
The present invention relates to rubber parts for aircraft. More particularly, it relates to rubber parts used as sealing components (e.g., aircraft O-rings, packings, gaskets, face seals) which come into contact with substances such as engine oil and jet fuel.
2. Prior Art
Rubber parts for aircraft, especially those used as fluid sealing components around jet engines, include O-rings (e.g., fluid line O-rings), seals (e.g., face seals, packings, gaskets), diaphragms and valves for aircraft engine oils, jet fuels, hydraulic oils and aviation hydraulic fluids such as Skydrol.
During use, such rubber parts often inevitably come into contact with fluids used in aircraft, such as engine oils (e.g., Mobil 254), jet fuels, hydraulic oils, and aviation hydraulic fluids such as Skydrol. To ensure normal operation, these aircraft parts are required to be resistant to jet fuels, resistant to carboxylic acids that arise from the oxidative degradation of synthetic oils (e.g., engine oils), resistant to amines and oils, and also resistant to gas permeability, heat and water. In addition, because aircraft are commonly operated in cold regions and at altitudes where low temperatures prevail, such rubber parts must also have a good cold resistance.
Hence, these aircraft parts are generally made of such materials as vinylidene fluoride-hexafluoropropylene copolymer-based fluororubbers, vinylidene fluoride-ethylene tetrafluoride-perfluorovinyl methyl ether copolymer-based cold-resistant fluororubbers, or fluorosilicones.
Vinylidene fluoride-propylene hexafluoride copolymers, though endowed with excellent heat resistance, resistance to oil and gasoline, and flexing resistance, lack sufficient cold resistance. The lower limit in their service temperature is xe2x88x9220xc2x0 C. for static sealing applications, and xe2x88x9210xc2x0 C. for dynamic sealing applications (e.g., diaphragms). In addition, such copolymers undergo considerable swelling in alcohols and ketones, becoming unfit for use thereafter. They are also subject to severe deterioration by amine-based additives in lubricating oils. Vinylidene-fluoride-ethylene tetrafluoride-perfluorovinyl methyl ether copolymers can be used at temperatures down to xe2x88x9230xc2x0 C. in static sealing applications, and down to xe2x88x9225xc2x0 C. in dynamic sealing applications, but even this falls short of cold resistance requirements today. Apart from their cold resistance, these copolymers have the same drawbacks as vinylidene fluoride-hexafluoropropylene copolymers.
Fluorosilicones have an excellent cold resistance, but an inadequate resistance to amines. In addition, they have a poor resistance to gas permeability and a poor water resistance.
A need has thus been felt for rubber parts endowed with each of the above properties to the desired degree.
It is therefore an object of the invention to provide rubber aircraft parts which are endowed with good resistance to jet fuels, jet engine oils, amines and oils, good resistance to gas permeability, good resistance to heat and water, and also outstanding cold resistance.
We have found that rubber aircraft parts endowed with good resistance to jet fuels, jet engine oils, amines and oils, good resistance to gas permeability, good heat and water resistance, and excellent cold resistance, can be obtained by using the cured form of a curable composition which includes a perfluoropolyether polymer of perfluoropolyether backbone having at least one reactive group, a crosslinking agent for crosslinking the polymer, and a silica filler having an average particle size of 0.001 to 10 xcexcm. In addition, we have discovered that such parts can be imparted with a dramatically improved low-temperature sealability at temperatures below the minimum service temperatures normally achievable in prior-art low-temperature fluororubbers, i.e., at xe2x88x9225 to xe2x88x9255xc2x0 C., particularly in a dynamic state, and can also be imparted with a markedly improved resistance to amines and other chemicals, thus making it possible to reliably ensure the sealability of fluid line junctions in jet engines.
Accordingly, the invention provides rubber aircraft parts which are made of the cured form of a curable composition that includes a perfluoropolyether polymer having a perfluoropolyether backbone and at least one reactive group, a crosslinking agent for crosslinking the polymer, and a silica filler having an average particle size of 0.001 to 10 xcexcm. The invention also provides a method of using the above cured product as a fluid sealing component around a jet engine.